The present invention relates to a table saw system, and more particularly to a fence for use with such systems for maintaining parallelism in objects to be cut when moved relative to a planar saw blade.
It is necessary in such systems to keep the fence parallel to the plane of the saw blade to insure the straightness of cuts and the avoidance of oblique angles. Even minor variations in such parallelism can lead to an unacceptable degree of error in cutting wood to be used for various carpentry applications. The problem is magnified if one attempts to remove the fence, for example, to cut a large piece of plywood or fiberboard, and then replace the fence to resume the cutting of smaller pieces. Some systems do provide for the removal and replacement of the fence, but suffer a loss of parallelism in the process. Others maintain parallelism but are difficult to remove and reinstall.
For example, the U.S. Pat. No. 2,166,703 to Boice shows a removable fence for a table saw system. The fence, however, is removed only by unscrewing small attaching parts such as nuts and bolts which can easily be lost. Other devices are easily removable but maintain parallelism by use of the "T square" principle. According to this type of device, parallelism is maintained by exerting pressure on a rail located parallel to the edge of the table. The fence is mounted on a member that slides along the rail and is arranged to be perpendicular to the member. The theory of this device is that once the member exerts pressure against the rail, as by gripping it with a cam and lever arrangement, the fence must be parallel to the saw blade since it is mounted perpendicular to the member. Examples of such systems are shown in the U.S. patents to Tautz, No. 2,235,082, Beisemeyer, No. 4,206,910, and Modderman, No. 2,556,548. These systems, however, all suffer from a common defect known as "cocking." Cocking is the natural tendency of the side of the fence opposite the gripping mechanism to drift slightly out of parallelism when gripping force is applied. Cocking results from the fact that a gripping force applied in a direction substantially parallel to the fence will, in fact, have small non-parallel components. Cocking even occurs in mechanisms adapted for simultaneous gripping on both sides of the fence such as the Modderman '548 patent, mentioned above.
Cocking, however, can be eliminated by using a flexible cable system in which these non-parallel force components on the cable are transmitted in the same longitudinal direction due to the manner in which the cable is strung. Drawing table arrangements have, in the past, used continuous loop cables mounted about the periphery of the table to which a straight edge can be attached. Examples of such systems are shown in the U.S. patents to Goodwin, No. 316,538, Vielhaber, No. 533,387, and Droste, No. 2,805,479. Vielhaber and Goodwin show what will be referred to herein as a continuous loop cable system. In systems of this type, a continuous strand of cable is mounted on pulleys arranged in a U-shaped fashion about the periphery of the drawing table. The pulleys are arranged such that the outer strands of the cable on opposite sides of the table are parallel and move in the same longitudinal direction upon movement of the straight edge which is attached thereto. Another example of this type of system is shown in the U.S. patent to Hochstatter, No. 3,656,390, in which a fence mounted on a continuous loop cable system is positionally adjusted by bringing a lever into abutment with a series of stops located at the front of the table. The fence, however, is not removable from the cable except by unfastening bolts which hold the fence to a cable-gripping slide and runner arrangement. Since any device used to grip the cable will necessarily impart at least a small force component running longitudinally with the cable, that is along its axial line, this force, exerted on a cable on one side of the table, will be transmitted via the cable itself to the other side, and in the same direction. Thus, no cocking occurs. This principle also permits the straight edge to be moved along the table while fastened to the cable system without losing parallelism. A variation of this concept is shown in the Droste '479 patent in which two endless loop cables are attached on opposite sides of the table to pulleys interconnected by a drive shaft connecting two of the pulleys. Any force on one set of cables is transmitted to the other via the drive shaft.
In these systems the straight edge can be set for parallelism, however, once set, cannot be removed without considerable difficulty in repositioning the straight edge. Once the straight edge is removed, paralellism is lost and a user must realign the straight edge to the table when he wishes to replace it. Moreover, in these systems, the straight edge is held in parallel relation to the table by gripping the wire or cable at various points. This gripping and loosening of the cable by locking nuts or pins leads to unacceptable depressions and stress points in the cable and makes it harder to continuously readjust the fence when the cable becomes well used. Also, such straight edge systems are not designed to hold the straight edge in rigid relation to the table. If the only connection between the straight edge and the table is the gripping of the wire by the straight edge or some device connected to it, the straight edge will lack the rigidity necessary in a table saw where considerable amounts of force are placed on the fence when guiding objects along it to be cut by the saw.